1. Field of the Invention
The present invention relates to an inkjet printhead board and to an inkjet printhead using same.
2. Description of the Related Art
The inkjet printer is of so-called a non-impact print scheme, having features of capable of printing at high speed, capable of printing on various recording media, and less causing noise upon printing. From those, the inkjet printer is broadly employed on an apparatus acting for a print mechanism, e.g. a printer, a copier, a facsimile machine or a word processor.
As for the inkjet printhead, there are known various schemes in respect of forming an ink droplet to eject. Among those, the inkjet printhead utilizing heat as ink-ejection energy realizes comparatively easily a multi-nozzle structure with high density, thus allowing for printing with high resolution and image quality at high speed.
There are cases that a ROM (read only memory) is mounted on a printhead in order to readably store information unique to the printhead, including printhead ID (identity) code and ink ejection mechanism drive characteristics. This function is very effective means in acquiring information unique to the printhead during printing and effecting drive optimally where a removable inkjet printhead is used on the inkjet printer body. For example, Japanese Patent Laid-Open No. H3-126560 discloses that an EEPROM (electrically erasable programmable ROM) is mounted on the printhead. However, in the printhead of Japanese Patent Laid-Open No. H3-126560, the EEPROM is mounted not on the printhead board but separately from the printhead. This makes structure complicate and productivity not well, thus hindering the size and weight reduction of the apparatus. Furthermore, such a ROM is useful in storing a great capacity of information but is not favor in respect of cost where information to store is not great in capacity.
Meanwhile, U.S. Pat. No. 5,363,134 and U.S. Pat. No. 5,504,507 disclose that a ROM having a fuse array is formed together with an ink ejection mechanism layer film on its base plate, i.e. a printhead board. In this case, when forming a layer film having an ink ejection mechanism, etc. on the base plate in the manufacture process of a printhead board, a fuse array to turn into a ROM can be formed at the same time. For example, in case a logic circuit is formed simultaneously with the fuse array and the fuses are selectively blown by controlling the logic circuit after completing a printhead, 2 values information can be held on the fuses in accordance with a presence/absence of meltdown. The printhead having a ROM on its printhead board does not require the preparation of a ROM chip separately from the printhead board, thus being not complicated in structure, well in productivity and realized in reduced size and weight.
FIGS. 10A and 10B are sectional views showing a printhead of an existing inkjet recorder having a ROM on its printhead board. FIG. 10A illustrates the usual state of the printhead while FIG. 10B the state that cracks are caused in an interlayer insulation film 804 and protection film 806.
In the usual inkjet printer, its printhead has a surface formed as an ink holder in the greater part thereof. As can be seen from FIG. 10A, the interlayer insulation film 804 and the protection film 806 exist between a fuse element 803 and an ink liquid 808. Although the fuse element 803 is shown only one in FIG. 10A, a plurality of fuse elements are practically provided on the printhead board. By selectively blowing the fuse elements, data can be held thereon in an amount of square of the number of the fuse elements.
However, heat is involved in blowing the fuse elements wherein, as the fuse elements increase in the number, a greater amount of heat inevitably occurs correspondingly. And there are possibilities that cracks possibly occur in the interlayer insulation film 804 and protection film 806, as shown in FIG. 10B. Where cracks are caused in this manner, ink 808 possibly permeates through the crack and reaches the fuse element 803. It can be considered that, by the permeated ink 808, the blown fuse element 803 is short circuited or a fuse electrode is eroded. Particularly, where a logic circuit for controlling to blow the fuse elements or to read data is arranged close to the fuse element, the ink intruding through the crack reaches the logic circuit resulting in a possibility to pollute the logic circuit and raise a malfunction.
In order to avoid this, Japanese Patent Laid-Open No. 2000-127403 describes a structure that an ink holder, a fuse array and a logic circuit are arranged separate to prevent ink from intruding.
However, the printhead in the recent has a plurality of ink supply openings and a plurality of heaters densely arranged corresponding to the ink supply openings, on one base plate constituting a printhead, in order to meet the demands for higher resolution, image quality and operation speed. Consequently, the base plate for use in a printhead is occupied in greater part thereon by a heater power line, a logic circuit, drive elements, etc., thus making it difficult to arrange an especial fuse element in a position distant from the ink holder.